The present invention relates broadly to a construction method for E-beam laser windows, and in particular to an apparatus and a process for soldering and contouring foil E-beam windows for excimer lasers.
In the prior art, previous foil prestrain techniques or procedures consisted of first soldering a section of foil material flat onto the cooling ribs on an excimer laser E-beam window. The spacing of nickel plating or solder strip on the foil material was identical to the spacing of the rib member. Then high pressure and high heat with hot oil were applied to the foil material to strain or stretch the foil into the desired shape. It has since been shown that this procedure significantly weakens the foils and reduces fatigue lifetimes. In addition, the presence of hot oil adds a greater risk that the foil material and the cooling rib to which it is attached, will become contaminated.
The state of the art of foil soldering techniques is well represented and alleviated to some degree by the prior art apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 3,650,017 issued to Gal on Mar. 21, 1972; PA1 U.S. Pat. No. 3,979,042 issued to Peters on Sept. 7, 1976; PA1 U.S. Pat. No. 4,072,262 issued to Godrick et al on Feb. 7, 1978; PA1 U.S. Pat. No. 4,347,965 issued to Grossman et al on Sept. 7, 1982; PA1 U.S. Pat. No. 4,558,736 issued to Ziemek on Dec. 17, 1985; and PA1 U.S. Pat. No. 4,587,701 issued to Koisuka et al on May 13, 1986.
The Gal patent discloses a process for coating a workpiece of light metal or light metal alloy with soft solder which comprises working those surfaces of the workpiece which are to be coated in an oxygen-free medium and while excluding oxygen therefrom contacting said workpiece with a soft solder bath.
The Peters patent describes a method for vacuum brazing nickel to aluminum. The outer surface of the aluminum member to which the nickel member is to be brazed is precoated with a layer containing silicon and magnesium. The nickel and aluminum members are placed together in an oven at reduced pressures and heated to a temperature of approximately 593.degree. C. cracking the oxide coating upon the aluminum sheet. The presence of magnesium and silicon in the surface of the aluminum sheets makes possible an excellent braze with a large filleted area.
The Godrick et al patent is directed toward a method of fabricating a solar heating unit having tubular conduits for containing high pressure fluids is disclosed. The method comprises the steps of forming a thin sheet of soft metal, preferably a fully annealed copper sheet, by applying sufficient temperature and pressure to creep or thermally form the sheet in a grooved plate using an assembly of fluid conduits having a paste solder applied thereon. The solder is melted during the creep forming step to form a good metallurigical bond between the sheet and the conduits.
The Grossman et al patent relates to a method of connecting thin metal sheets to metal tubes to form a solar collector plate which is carried out by explosive bonding to ensure a high thermal conductivity between sheet and tubes. The sheet is prepressed in a pattern of channels of substantially semicircular cross section conforming to the shape of the tube grid. A heavy supporting plate is provided, in its flat surface, with a similar pattern of channels, but in mirror symmetry; the tubes of the grid are completely filled with water and the grid is laid into the channels of the supporting plate. Then the grid is covered by the sheet, with the channels covering the tubes and the flat sheet portions in contact with the surface of the supporting plate. Explosive charges in ribbon shape are laid onto the sheet along the pieces of all channels on their outside, and the charges are detonated, whereafter the joined grid and sheet are removed from the plate.
The Ziemek patent presents a method of manufacture of a heat exchanger, particularly for solar collectors wherein a metal plate is continuously longitudinally welded to a metal tube centrally between the longitudinal edges of the plate. The width of the metal plate is greater than the outer diameter or cross sectional dimension of the tube and the metal plate is plastically deformed in deformation areas on both longitudinal sides so as to increase its surface in these respective areas between its longitudinal edges and short of the longitudinal line of welding contact with the tube. An undeformed region extends in the longitudinal direction of the tube between the deformation areas.
The Koisuka et al patent describes a method for producing an aluminum heat exchanger wherein a serpentine-type aluminum heat exchanger comprises a serpentine-anfractuous flat tube of an aluminum alloy, a plurality of corrugated fin units made of an aluminum alloy having a high aluminum content of 99 wt. % or more, and brazing metal coating layers fixed onto entire flat surfaces of parallel portions of the serpentine-anfractuous flat tube and for joining the flat tube and fin units, is produced by preparing the serpentine-anfractuous flat tube of an aluminum alloy, the corrugated fin units and U-shaped members of an aluminum alloy brazing filler metal, closely fitting the U-shaped members onto the parallel portions of the flat tube, disposing the fin units in spaces between adjacent U-shaped members fitted onto the parallel portions of the flat tube, and heating the flat tube, the fin units and U-shaped members in the assembled relation to the brazing temperature.
In the construction of E-beam windows for excimer lasers, a thin foil is soldered to a cooling rib support structure. It is important to the life and operation of the laser that the window foil is not weakened by this construction procedure, because long foil fatigue lifetimes are desireable in E-beam window designs for excimer lasers. In order to achieve E-beam windows with long fatigue lifetimes, the foil and the solder must be contoured to match the curvature of the rib surface, and also the foil must be curved in-between the ribs. This contouring reduces stress in the foil at the solder edge as well as increases the ability of the foil to resist thermal buckling. The problem is to obtain the desired foil contouring, without weakening the foil in the process. The present invention is directed to the method and apparatus of foil soldering and the contouring process to make E-beam windows for an excimer laser which will overcome some of the shortcomings of the prior art.